Center pins are used, e.g., to accurately align two components to be connected to one another in a flange-like manner. For example, gear casings are placed in an accurately aligned manner on an engine block of a motor vehicle engine via center pins and are fastened to the engine block by means of bolts. The center pins are regularly pressed into corresponding mounting holes of, e.g., the engine block. To make it possible to replace the center pins, these must be removed from the press fit and pulled out of their mounting holes. Special tongs, which are provided with corresponding gripping elements and by means of which extremely strong clamping forces can be applied for gripping a straight pin, are conventionally used for this purpose. Since the straight pins are seated extremely firmly in their mounting holes, blows are applied to the tongs with a hammer in the direction of extraction, so that the corresponding straight pin is released from the mounting hole and extracted millimeter by millimeter. If such tongs are provided with a self-locking mechanism, tire levers are usually used to release and extract the straight pin, and these tire levers are supported on the engine block during the extraction operation and grip behind the gripping elements of the tongs. However, damage to the surface of, e.g., the engine block around the area surrounding the mounting hole must always be expected to occur in the process, so that this method cannot be recommended.
Furthermore, such straight pins are also provided for the accurate mounting of flywheels on the front side of a crankshaft, which also must be released and extracted when needed. Another problem with the extraction of such straight pins is their accessibility. It is extremely difficult to strike the gripping elements of the tongs with a hammer in the installed state. This also applies to the lever method.
The removal of hardened straight pins from the fitting holes of aluminum engine blocks is especially problematic. Since the straight pins are seated in very deep fitting holes in these cases, the extraction of such straight pins is not possible with the methods described at all. This is also due, in particular, to the fact that these hardened straight pins are harder than the gripping jaws of the tongs used, so that these tongs with their gripping jaws always slip off from the straight pins and the aluminum engine blocks cannot therefore be used anymore, because the straight pins cannot be removed and replaced with new ones.
Furthermore, there also are other components which are pressed into a corresponding mounting hole in the normal operating state and must be replaced when needed. Such components include, e.g., injection nozzles, which are arranged integrated in the motor housing in the area of the crankshaft of the engine. Such injection nozzles are used, e.g., to lubricate and cool the pistons of the engine. These injection nozzles also must be extracted from their mounting holes in case of damage, which is associated with the additional problem that these injection nozzles are arranged recessed in the inner area of the engine block and access to them is very difficult. These injection nozzles usually have a cylindrical section, with which they axially protrude from their mounting holes and can thus be gripped with tongs or a similar tool. The injection nozzle is usually provided in the area of this cylindrical section with a nozzle tube, which initially extends radially and is then bent toward the piston, so that this makes the access additionally difficult.
Another disadvantage of the hitherto known processes and methods for extracting straight pins is that the holding forces of the gripping element are often insufficient to perform the extraction in one operation. It is therefore often necessary to change the grip on the straight pin with the gripping element, because the gripping element slips off the straight pin, especially if it is struck with a hammer. This happens especially in the case of hardened straight pins installed in an aluminum housing, as was already described above in connection with aluminum engine blocks.
For example, a device with which drive shafts mounted recessed in a depression of a housing can be extracted is known from, e.g., U.S. Pat. No. 5,727,298 for making it possible to apply stronger holding forces. A tubular basic body is provided here, which is provided at one of its ends with gripping elements, which have an outer jacket surface widened conically radially toward the end. This basic body is received with its gripping elements in the mounting hole of a guide tube in an axially adjustable manner. The mounting hole has a conical inner surface in the axial end area of the gripping elements, so that when the basic body with its gripping elements is pulled into the hole with its conical section, the gripping elements are pressed radially inwardly with their conical section. If the gripping elements, which define a cylindrical hole between them, are seated on the drive shaft, the radial adjustment of the gripping elements brings about a clamping force between the gripping elements and the drive shaft. To make it possible to pull the basic body with its gripping elements into the hole of the guide tube, the basic body is provided with a threaded section at its end located opposite the gripping elements. This threaded section protrudes from the guide tube, so that a tensioning nut can be screwed on. When the tensioning nut is tightened, the basic body is pulled with a strong force into the guide tube. Once this tool is seated firmly on the drive shaft, the drive shaft can be extracted. A plurality of pressing screws screwed into a radially outwardly protruding flange of the guide tube are provided for this purpose. The flange is arranged in the area of the threaded section of the basic body, so that the guide tube protrudes into the depression of the housing. The pressing screws are supported for the extraction at the edge of the area surrounding the depression. When these pressing screws are tightened, the guide tube is extracted from the depression together with the basic body and its gripping elements, so that the drive shaft is also inevitably removed from its hole. Only very specific drive shafts arranged in a depression can be extracted with this prior-art device. Furthermore, both the device and the housing or the depression in the housing may be damaged if the pressing screws are not tightened uniformly. If, e.g., only one of the pressing screws is tightened very tightly at the beginning of the extraction operation, this leads to damage to the surface of the housing and also to damage to the drive shaft, because the pulling force acts obliquely in relation to the direction of the axis of the drive shaft. Furthermore, the extraction is very time-consuming, because the pressing screws can always by tightened by a minimum amount one after another in order to prevent such damage. This means that even though this device could apply the necessary clamping forces for gripping a drive shaft, the handling of the device is extremely time-consuming and complicated.